1. Technical Field
The present invention relates to a projecting zoom lens having six groups and mounted on a projection type display device or the like and to a projection type display device having the projecting zoom lens mounted thereon and, more particularly, to a projecting zoom lens and a projection type display device for magnifying and projecting such a luminous flux on a screen carrying video information from a light valve of a liquid crystal display device or a DMD (Digital Micromirror Device) display device.
2. Related Art
In recent years, there becomes widespread the projection type display device using the light valve such as the liquid crystal display device or the DMD display device. This widely used device is constituted such that three light valves are used to correspond respectively to the illuminating lights of the three primaries RGB thereby to modulate those illuminating lights, and such that the lights modulated by the respective light valves are synthesized by a prism or the like and are displayed through a projection lens on a screen.
In the light valves described above, the size reduction and the high precision advance abruptly, and the personal computers become widespread. As a result, the demands for presentations using that projection type display device are rising. Thus, the projection type display device is demanded to have a higher performance, a smaller size and a lighter weight.
In the projection type display device, in which the respective modulated lights from the three light valves are synthesized and projected by a color synthesizing optical system, the projecting lenses requires long back focuses to arrange prisms for the color synthesization. In the color synthesizing optical system, moreover, the spectroscopic characteristics are changed by the angles of incident lights, so that the projecting lenses requires the characteristics, in which the incident pupils seen from the reduction side are sufficiently distant, that is, the telecentricity. There are further needed bright lenses and aberration corrections matching the resolution of the device. In the case of the front type, the zooming function and the wide-angle of view are also demanded from the viewpoint of mountability. In accordance with the size reduction of the light valve itself, the increased demand for the mobile application and the reduced price of the projector, moreover, there is a tendency to demand the smaller size and lighter weight form the projection lens.
As the projection lens capable of satisfying those demands, there are known a number of zooming types (as referred to Patent Documents 1 (JP-A-2004-138812)and 2 (JP-2006-162734), for example), in which the lenses are composed of, in order from the magnification side, five groups of negative—positive—positive—positive (or negative)—positive such that the second, third and fourth lens groups are moved during zooming along the optical axis, and the first lens group and the fifth lens group are fixed.
In the following Patent Documents 3 (JP-A-2006-184723) and 4 (JP-A-2006-317976), for example, there are another zooming type, in which the lenses are composed of, in order from the magnification side, six groups of negative—positive—positive—positive—positive (or negative)—positive and the first lens group and the sixth lens group are fixed.
It is known that the performance of a lens may be improved if the degree of freedom for optical designs may be raised by increasing the number of lens or the zoom moving groups. However, the increase in the number of lens portions leads directly to the upsizing of the device or the rise of the cost, and the spectral transmittance is lowered if the thickness of the glass material of the entire lens system increases. The drop of the spectral transmittance is serious especially on the shorter wave side, and is disadvantageous especially in the projecting optical system, for which it is difficult to adjust directly the projected image having passed through the projection lens.
The present invention has been conceived in view of the background thus far described, and has an object to provide an inexpensive projecting zoom lens, which can hold the telecentricity on a reduction side while achieving a wide-angle of view, which can correct satisfactorily various aberrations such as spherical aberrations, longitudinal chromatic aberrations and field curvatures, and which can achieve the size reduction even with high brightness and performance, and a projection type display device.